How to set instance IP address?

I'm trying to set up a live and a development tenant for an application, and to simplify development I would like to use the same IP addresses for VMs in both tenants. I created two subnets with the same IP address pool, but when I spin up instances they get a random IP address from the pool. How can I change that address so that VMs in my dev and live environment can have the exact same IPs?

I tried to diasable DHCP, but it didn't work. The instances stillg get an ip address in OpenStack, and I can not change that. The instances however do not get this address via dhcp as it is switched off. If I configure an IP address other than what is specified in OpenStack the connection breaks.